1. Field of the Invention
The present invention relates to a waveguide circulator, and more particularly to a three-junction waveguide circulator used suitably for high-power microwave.
2. Description of the Related Art
In recent years, it is known that a field wherein microwave power is used becomes expanded widely over various industrial fields.
Particularly, since electric power to be applied is raised from several kW to around several MW in a frequency band of UHF band or a higher band, it is desired to develop a high-performance circulator which can respond to such a large amount of power as described above.
In the following, a conventional waveguide circulator will be described by referring to FIGS. 1(a) and 1(b).
Namely, FIG. 1(a) is a plane explanatory view showing a conventional three-junction waveguide circulator, and FIG. 1(b) is a sectional explanatory view taken along line A-A of FIG. 1(a).
The conventional three-junction waveguide circulator 10 shown in FIGS. 1(a) and 1(b) is composed of a waveguide 12 formed substantially in Y-shape with rectangular waveguides 12-1, 12-2, and 12-3 which are provided so as to position horizontally on a predetermined plane, and further they are extended in different three directions from positions of the junctions, respectively; a cylindrical column-shaped pedestal 14 disposed on the undersurface 12aa of the waveguide 12 in the junction positions in an inner circumferential surface 12a thereof; a column-shaped pedestal 16 disposed on the upper surface 12ab of the waveguide 12 in the junction positions in the inner circumferential surface 12a so as to be opposed to the upper surface 14a of the pedestal 14; a circular disc-shaped ferrite member 18 adhesively fixed on the upper surface 14a of the pedestal 14; and a circular disc-shaped ferrite member 20 adhesively fixed on the under-surface 16a of the pedestal 16.
According to the above-described construction, an S-pole magnet 22 is placed under the lower side of the position at which the pedestal 14 is disposed so as not to be in contact with the outer circumferential surface 12b of the waveguide 12, and further an N-pole magnet 24 is placed over the upper side of the position at which the pedestal 16 is disposed so as not to be in contact with the outer circumferential surface 12b of the waveguide 12 outside the same in the waveguide circulator 10.
Magnetic field is induced by the S-pole magnet 22 and the N-pole magnet 24 in the junction positions of the waveguide 12, whereby the ferrite members 18 and 20 fixed adhesively to the pedestals 14 and 16, respectively, are magnetized.
In these circumstances, when electromagnetic wave such as microwave passes through the junction positions in which the ferrite members 18 and 20 under the magnetized state are positioned, a course of the electromagnetic wave passed through the junction positions is curved diagonally forward left while keeping polarization plane horizontal.
More specifically, when the electromagnetic wave which enters through the rectangular waveguide 12-1 passes through the junction position at which the ferrite members 18 and 20 are positioned wherein these ferrite members 18 and 20 have been in magnetized state, the electromagnetic wave which was thus passed through the junction position goes into the rectangular waveguide 12-2.
In a similar fashion, when the electromagnetic wave which enters through the rectangular waveguide 12-2 passes through the junction position at which the ferrite members 18 and 20 are positioned wherein these ferrite members 18 and 20 have been in magnetized state, the electromagnetic wave which was thus passed through the junction position goes into the rectangular waveguide 12-3.
Furthermore, in like wise, when the electromagnetic wave which enters through the rectangular waveguide 12-3 passes through the junction position at which the ferrite members 18 and 20 are positioned wherein these ferrite members 18 and 20 have been in magnetized state, the electromagnetic wave which was thus passed through the junction position goes into the rectangular waveguide 12-1.
However, the ferrite members 18 and 20 generate heat due to the heat generated by internal insertion loss of the ferrite members with increase of electric power applied in the above-described waveguide circulator 10.
Thus, there is such a problem that when the ferrite members 18 and 20 generate heat, saturation magnetization 4 πMs in the ferrite members 18 and 20 decreases, whereby microwave characteristic in the waveguide circulator 10 becomes inferior.
Furthermore, there is such another problem that when electric power to be applied in the waveguide circulator 10 increases, arcing (abnormal discharge) phenomenon appears between the ferrite members 18 and 20.
In this connection, it is known that a distance between the ferrite members 18 and 20 is constructed so as to extend as a countermeasure therefore as a countermeasure for the above-mentioned arcing phenomenon.
Referring to FIG. 2, there is shown an equivalent circuit diagram of an ideal waveguide circulator. An explanation is made with reference to FIG. 2 wherein when a distance between the ferrite members 18 and 20 is extended as a countermeasure for arcing phenomenon, stray capacitance C between the ferrite members 18 and 20 becomes small.
As described above, as a result of reduction of the stray capacitance C between the ferrite members 18 and 20, there is such a problem that impedance inside the waveguide circulator 10 decreases, so that fractional bandwidth of bandpass wherein a return loss is 26 dB or less becomes 3% or less, whereby the fractional bandwidth becomes narrow, even if an adjustment is made by a capacitive device or an inductive device from the outside of the waveguide circulator 10.
In other words, the following problems are pointed out with respect to a conventional waveguide circulator. In the conventional waveguide circulator, ferrite members generate heat with increase of electrical power to be applied, and it results in temperature rise of the ferrite members. For a countermeasure against arcing phenomenon, when a distance between ferrite members is extended sufficiently in such degree that no arcing phenomenon arises, a stray capacitance between the ferrite members becomes small. As a result, saturation magnetization 4 π Ms in the ferrite members decreases, and in addition, it results in deterioration of microwave characteristic such as deterioration of return loss and isolation.
It is to be noted that since the prior art concerning the present invention does not relate to an invention known to the public through publication, there is no information as to prior art literary document published to be described herein at the time when the present application was filed by the present applicants.